Morphometric evaluation of changes with time in optic disc structure and thickness of retinal nerve fiber layer in chronic ocular hypertensive monkeys

Abstract

Abstract: : Purpose: To examine the time course of changes in optic disc structure and retinal nerve fiber layer (RNFL) thickness [by means of a scanning laser ophthalmoscope (HRT) and a scanning laser polarimeter (GDx), respectively] in glaucomatous monkeys, and to clarify the relationships between the histological RNFL thickness and the HRT or GDx parameters. Methods: A chronic intraocular pressure (IOP) elevation was induced by laser trabeculoplasty in the left eye in 11 cynomolgus monkeys. In Exp. 1, the HRT and GDx parameters were measured 12 weeks after the laser treatment in 10 eyes in 5 monkeys. In Exp. 2, the time course of changes in the HRT and GDx parameters was examined during 16 weeks after the laser treatment in 12 eyes in 6 monkeys. Results: Changes in HRT parameters occurred rapidly during the first 4 weeks after the laser treatment, with little change being observed thereafter. The GDx parameters declined in a time–dependent manner alongside the IOP elevation. These parameters almost plateaued at about 8 weeks after the laser treatment. Significant correlations were seen between the histological mean RNFL thickness and the HRT or GDx parameters in 21 eyes from 11 monkeys. Especially good correlations with histological mean RNFL thickness were seen for the rim volume (ρ = 0.897, p < 0.001), cup volume (ρ = –0.899, p < 0.001), and modulation parameters (ρ = 0.946, p < 0.001 in inferior quadrant). Conclusions: Alongside the IOP elevation, time–related changes in optic disc topography and RNFL thickness were demonstrated in experimental glaucoma monkey eyes using HRT and GDx. HRT rim and cup parameters and GDx ratio and modulation parameters showed (a) good correlations with histological RNFL thickness, and (b) significant interrelations.

Keywords: imaging/image analysis: non–clinical • nerve fiber layer • optic disc